The project will investigate the effects of halothane on liver cell ultrastructure in rats that have been pretreated with phenobarbital and made hypoxic during halothane administration. The project will utilize a quantitative morphometric technique, described by Wiebel, to provide a numerical description of hepatic organelles with respect to hepatocyte cytoplasmic volume 2, 4 and 6 hours after exposure of phenobarbital pretreated rats to halothane with and without hypoxia. Additionally, microsomal cytochrome P450 will be assayed as an index of the effect of the treatments on the hepatic drug metabolizing enzyme system. SGOT and SGPT will be assayed as an additional index of hepatic cellular injury. The project will evaluate the suitability of this animal preparation as a model for the laboratory study of halothane provoked hepatic cellular damage. Data developed by this study will provide a basis for comparing the cellular morphologic effects of other anesthetic agents.